1. Field of the Invention
The present invention relates to a machine for coating, and particularly for sugar coating articles of confectionery or pharmaceutical or like products, such as, for example, almonds, hazel-nuts, biscuits, chewing-gum or other such comestibles, or pastille tablets, pills or other pharmaceutical preparations. Known prior art sugar coating processes essentially comprise a first stage in which articles such as one of the above-mentioned products, are coated with a fluid or semifluid substance comprising, for example, a solution, suspension or mixture of sugar and starch, and a second stage in which drying and crystallizing of the applied coating take place. Generally this second stage is carried out by means of a current of air, frequently heated air, which is directed over the coated articles.
When sugar coating is performed on an industrial scale various problems have to be overcome if uniform products with predetermined characteristics and properties are to be obtained. For example, it is necessary for each article to be coated as completely and uniformly as possible with the coating substance so that the final coating has no surface discontinuity despite the inevitable discontinuities in the surfaces of the articles to be coated. Moreover, it is necessary to prevent the articles in contact with one another from sticking together during the drying and crystallization of the coating since they would otherwise adhere together and form lumps which would have to be scrapped.
For this purpose the articles to be coated are kept in continual movement while being sprayed with the coating substance, and simultaneously a current of air is directed over them until crystallization of the sugar coating takes place.
2. Description of the Prior Art
Known prior art machines for coating articles such as are mentioned above with sugar, comprise essentially a receptable of stainless steel or copper, which is rotatable about a horizontal axis or an axis inclined to the horizontal by not more than 45.degree.. Receptacles of various shapes have been used, including cylindrical, spherical, egg-shape and cup-shape, receptacles.
Such a prior art receptacle has an aperture through which the articles to be sugar coated are loaded into the receptacle and, after treatment discharged from the receptacle, and is further provided with one or more ducts for feeding in the coating substance, and with one or more ducts for feeding in the air, which may be heated air, for the drying and crystallization of the coating. In operation of such a prior art machine the receptacle is loaded with a plurality of articles to be sugar coated, the quantity being such as will occupy only a small portion of the bottom of the receptacle. The receptacle is then rotated about its axis, and the articles therein are carried, in the same direction as the rotation, against the wall of the receptacle up to a certain height, after which they tumble over one another, returning to the bottom of the receptacle by rolling over the articles beneath, which are being carried along with the wall. Thus there is a continuous mixing of the article in the receptacle so that when a coating liquid is fed into the receptacle it is distributed over the articles by their tumbling action. Simultaneously with or subsequently to the intake of the coating substance, the container is fed with a current of air, possibly heated air, which by penetrating between the moving articles causes the required drying of the coatings.
Such prior art machines, although widely used, have a number of technical and economical disadvantages which have hitherto not been overcome. For satisfactory operation of such a machine it is necessary that the articles loaded into the container should occupy only a small fraction of the total volume thereof. Furthermore, because of the characteristic shape of the containers hitherto used, and because of the particular motion of the articles when being subjected to treatment in these containers, it is not possible to obtain good physical and thermal contact between the air blown in for the drying and all the articles to be dried, the air tends to pass over only those articles on the surface at any one time and not penetrating into the center of the batch of articles in the machine. Consequently, in order to achieve satisfactory results, prolonged drying times of the material are required so that the machine must remain in operation for considerable periods of time. These two factors combine to restrict the output and the efficiency of the machine to a rather low value. A further disadvantage of known prior art machines lies in that fact that the tumbling movement of the articles within the container results in each article suffering a number of impacts with adjacent articles with consequential damaging effects of deformation or fracture, making it necessary to scrap a certain proportion of the output.
Another disadvantage of the conventional prior art types of machines is the laborious nature in which loading and discharging of the articles to be treated takes place through the single opening of the substantially closed container. These operations require the stopping of the machine, and are effected manually, they are thus labour intensive operations in which operating time of the machine is lost, thereby being doubly disadvantageous.